Everyone except external users and Everyone claims added by default when new site is created in SPO

[SenthilrajanKaliyaperumal]

Hi,

I have created sites( private team site, public team  site and communication site) in my tenant, and noticed that below users/groups added by default.  I can see all these entries in user info list or all people list(_layouts/15/people.aspx?MembershipGroupId=0)

1. Everyone except external users
2. Everyone
3. Site owner/creator name
4. O365 group members if it is group site

I understood the purpose of 3 & 4 but not clear why 1&2 are added by default to the sites.

Please explain why 1&2 are added in to private group site when site is created.

Thanks in advance.